The present invention relates generally to broadband and wireless communications and more particularly to link adaptation for LTE/LTE-A uplink with a turbo receiver.
Closed-loop link adaptation enabled by adaptive modulation and coding scheme (MCS), rank adaptation and precoding matrix index (PMI) selection are known to be an effective technique to further enhance the performance of wireless systems with multiple antennas. For the systems with linear multiple input multiple output (MIMO) receivers, a post-processing signal-to-interference-plus-noise-ratio (SINR) of the equivalent scalar additive white Gaussian noise (AWGN) channel is available. MCS assignment and PMI/Rank selection can easily be done based on this effective post-processing SINR. However, the rate adaption (MCS assignment), rank adaptation and PMI selection for the systems equipped with non-linear receivers such as turbo MMSE-SIC (minimum mean square error—successive interference cancelation) is non-trivial since there is no explicit effective SINR expression for the turbo SIC output. The potential gains enabled by advanced receivers cannot be realized if the post-processing SINRs assuming linear MIMO receivers are used for closed-loop link adaptation.
One simple but conservative rate adaptation scheme is to determine MCS, PMI and rank based on linear minimum mean square error (MMSE) SINRs. This method is simple but too conservative to sufficiently claim the performance gain provided by advanced receivers.
In another prior disclosed technique, a Gaussian approximation method is proposed to predict iterative turbo MMSE-SIC performance. This method assumes that the residual interference seen by each distinct codeword after soft-cancelation at each iteration is independent and Gaussian. Further, it relies on a one-dimensional look-up table (LUT) to compute the variance of this residual interference. The effective SINR can then be analytically computed based on the channel realization and the residual interference variance. However, for this method a big mismatch between the predicted performance and actual performance is observed. In addition, the rate assignment has very high complexity and low flexibility since the, MCS assignments for different codewords are coupled.
Accordingly, there is a need for improved adaptation for an LTE/LTE-A uplink in a wireless communication system.